Cord driving mechanism for a blind

ABSTRACT

A cord driving mechanism for a blind is described, which comprises a cord driving pulley having a circumferential, radially outward-facing groove comprising a plurality of nips, the nips defined by formations which are disposed opposite one another on respective sides of the groove and are positioned so that the path of a cord around the pulley is relatively straight and so that the cord is substantially unconstricted in the regions between the nips; and a shoe, relative to which the pulley rotates, which surrounds at least part of the circumferential groove in the pulley. A cord passes around the pulley, in the space defined by the circumferential groove and the shoe. The cord is retained in the groove by contact with the shoe. The dimensions of the groove, the spacing between the groove and the shoe, and the size of the cord provide a desired resistance to rotation of the pulley and a desired maximum load which can be exerted on the cord.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of International application numberPCT/GB97/00626, filed on Mar. 7, 1997, and published as WO 97/33064,which in turn claims the benefit of UK application GB 9604861.6, filedon Mar. 7, 1996.

FIELD OF THE INVENTION

This invention relates to powered blinds of the type which includes anoperating cord entrained around a powered driving pulley. In the case ofvertical blinds, the cord may operate the open/close function of theblind.

BACKGROUND

Power is delivered to the pulley from an electric motor via a gearboxand rotation of the pulley tends to entrain the cord, thus operating theblind. However, to ensure that the cord is reliably gripped by thepulley, it has hitherto been found necessary to ensure that the cord istensioned in its passage around the pulley. Clearly, once the pulleybegins to drive the cord, there will be a certain amount of tension inthe cord upstream of the pulley, but it has been found that tension(additional to that resulting from the weight of the cord itself) isrequired both upstream and downstream of the pulley to ensure that asthe pulley begins to rotate, it takes the cord with it. This will bereferred to as “back-tensioning” of the cord. It gives rise to excessivewear on the pulley bearings and increases the drag of the mechanism,thereby increasing the motor current required to drive the blinds

Furthermore, the task of assembling the driving mechanism of the blindrequires a degree of dexterity, since the cord must be kept properlypositioned relative no the pulley until the cord can be tensioned tokeep it in place.

SUMMARY

It is an object of the present invention to address the problemsoutlined above.

According to a first aspect of the present invention, there is provideda cord driving mechanism for a blind comprising a cord driving pulleyhaving a circumferential, radially outward-facing groove and a shoe,relative to which the pulley rotates, surrounding at least part of thecircumferential groove in the pulley. The advantages of this arrangementare twofold. Firstly, the shoe will retain the cord positioned correctlywith respect to the pulley during the manufacturing process. Secondly,the shoe can be arranged to bear against the cord to ensure that it isproperly gripped by the pulley as the pulley begins to rotate inservice. The net result is that much less, or no, back-tension isrequired, the pulley bearings will last longer and the drag of themechanism will be considerably reduced.

For extra security, it is preferred that the shoe should surround atleast half of the circumference of the pulley. This has furtheradvantages which will be explained later.

In a preferred arrangement, a plurality of nips are distributed aroundthe circumferential groove of the pulley. These nips pinch the cord asit passes around the pulley, ensuring a further improvement in theability of the pulley to grip the cord. Each of the nips is preferablyradial within the groove. The nips are preferably spaced equidistantlyaround the circumferential groove.

To ensure that at least one nip grips the cord at any time, there shouldbe at least four. For example, there may be twelve.

To ensure a good grip on both sides of the cord, it is preferred thatthe nips be defined by formations on both sides of the circumferentialgroove. For example, the formations defining each nip may be oppositeone another on each side of the groove. This arrangement keeps the pathof the cord relatively straight and provides unconstricted regionsbetween nips, one advantage of which will be described later.

The formations may be triangular teeth and are preferably symmetric,since the pulley will need to drive the cord in both directions.

The mechanism is preferably arranged to be self-threading (as will bedescribed later).

For reasons which are self-evident, the mechanism will benefit from adoctor arranged adjacent the circumferential groove in the pulley andadapted to guide the cord out of the groove when the pulley is rotated.Again, as two directions of rotation are required, the doctor ispreferably substantially symmetric. For reasons which will be explainedlater, the doctor may define an insertion opening for the cord.

According to a second aspect of the invention, there is provided a blindincluding a cord driving mechanism comprising a pulley having acircumferential, radially outward-facing groove and a shoe, relative towhich the pulley rotates, surrounding at least part of thecircumferential groove in the pulley and further including a cord whichpasses around the pulley, in the space defined by the circumferentialgroove and the shoe. The cord driving mechanism is preferably asdescribed above as being in accordance with the invention. The pulley isadapted to drive the cord which is, in turn, adapted to operate movingparts of the blind, such as the traverse or tilt mechanisms.

Preferably, the cord is not back-tensioned in normal use and this canbest be achieved by arranging for it to be retained in the groove bycontact with the shoe. The dimensions of the groove and/or the spacingbetween the groove and the shoe and/or the size of the cord may beselected to provide a desired resistance to rotation of the pulleyand/or a desired maximum load which can be exerted on the cord.

A third aspect of the present invention provides a cord driving pulleyfor a blind having a circumferential, radially outward-facing groovearound which are distributed a plurality of nips

A fourth aspect of the present invention provides a method of installinga cord in a cord driving mechanism of a blind comprising a cord drivingpulley having a circumferential, radially outward-facing groove and ashoe, relative to which the pulley rotates, surrounding at least part ofthe circumferential groove in the pulley, comprising offering a free endof the cord to the space defined by the circumferential groove and theshoe and rotating the pulley to entrain the cord. This is a much simplermethod than that currently in use. Because this method is envisaged, itis better for the shoe to surround as much of the circumference of thepulley as will carry cord in normal use, i.e. over half of it.

Where the mechanism includes a doctor arranged adjacent thecircumferential groove in the pulley and adapted to guide the cord outof the groove when the pulley is rotated, the method will furthercomprise retrieving the free end of the cord once it has passed aroundthe pulley and is freed by the doctor.

Where, as described above, the doctor defines an insertion opening forthe cord, the free end of the cord will be offered up to that opening.Similarly, where a plurality of nips are distributed around thecircumferential groove, the free end of the cord will be offered up tothe region of the groove between two of the nips.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of example withreference to FIGS. 1A through 5 of the accompanying drawings, in which:

FIGS. 1A through 1C show one half of a molded pulley;

FIGS. 2A through 2C show the other half of a molded pulley;

FIGS. 3A through 3C are an assembly drawing of the pulley;

FIGS. 4A through 4C show a molded doctor; and

FIG. 5 is an assembly drawing of a gearbox.

DETAILED DESCRIPTION

The half pulley 10 illustrated in FIGS. 1A through 1C comprises a flange12, shaped on one side 14 so as, in cooperation with the other halfpulley 16 illustrated in FIGS. 2A through 2C, to provide a “V”-shapedgroove 15 in the finished product, as illustrated in FIGS. 3A through3C. A central cylindrical bore 20 is provided in the flange, togetherwith locating features in the form of a pin 22 and a pair ofpart-cylindrical bosses 24. The side 14 of the flange 12 which forms onehalf of the “V”-shaped groove includes twelve symmetric, triangularteeth 26. The teeth and the flange have central, relatively shallowlyinclined surfaces 28, 30 and distal, relatively sharply inclinedsurfaces 32, 34. These help the teeth 26 and the groove 18 to grip thecord (not shown).

The half pulley 16 illustrated in FIGS. 2A through 2C also comprises aflange 36, shaped on one side 38 so as to cooperate with the other halfpulley 10 illustrated in FIGS. 1A through 1C. A central bearing surfacein the form of a cylindrical bore 40 is provided in the flange,continuing into a central boss 58, together with locating features inthe form of a recess 42 and a pair of part-cylindrical detents 44.Again, the side 38 of the flange 36 which forms one half of the“V”-shaped groove includes twelve symmetric, triangular teeth 46. Theteeth and the flange have central, relatively shallowly inclinedsurfaces 48, 50 and distal, relatively sharply inclined surfaces 52, 54.

The teeth 26, 46 in both pulley halves can be seen to be radiallydirected. It is for this reason that the pulley is manufactured in twohalves 10, 16. If this were not so, there would need to be as manyremovable cores in the mold as there are teeth on the pulley, twelve inthis example. This would increase both tooling and production costs. Atwo part molding is used to allow radial teeth, since it is clear that,in a pulley which must grip efficiently and operate in both directions,radial teeth are to be preferred.

The assembly of the pulley 56 is shown in FIGS. 3A through 3C. As willbe understood, on assembly, the central boss 58 will be received in thebore 20; the pin 22 will go into the recess 42: and the bosses 24 willgo into the detents 44. In this way the teeth 26 will line up exactlywith the teeth 46, to provide a series of nips 60, separated by spaces62. The finished pulley has an integral gear 64, molded integrally withthe second half 16. The two halves may be ultrasonically weldedtogether, although care must be taken to prevent distortion, or may beglued together. In either case, the amount of pressure applied will varythe separation between the teeth 26, 46, which may be significant.

The choice of material for the pulley and the choice of material for thecord are important. A balance must be struck between the need for goodgrip between the pulley and the cord and a desire to reduce abrasion ofthe cord. The presently preferred material for the pulley is DuPont'sMinlon 23B1, a 37% mineral-glass-reinforced PA (nylon) 66 (28% mineral,9% glass). This combines well with a 2.5 mm nominal diameter smoothbraided polyester cord with polyester filler, such as are well known tothose skilled in the art of blind making.

An important advantage of the present invention can be appreciated fromits ability to use unmodified polyester cords. Most motorised blinds usea drive train which can be described as incorporating a “positive drive”member. This member may take the form of a ball chain or an aperturedtape or a helical drive shaft. The present invention takes advantage ofunmodified cords, which it is able to do by virtue of its uniquenon-tensioned and self-threading construction. It is thereforeapplicable to the conversion of manual blinds to motorised form, not somuch as an after-market accessory, but rather as a convenient way formanufacturers to modify their own products. This carries with itsubstantial development cost advantages, as there is no need to modifythe perfectly good mechanism of a manual blind to accommodate anymodified motorised drive train.

FIGS. 4A through 4C illustrate a doctor 66. The doctor 66 includes ablade 68 which goes between the two parts 10, 16 of the pulley 56 toguide the cord out of the groove 18. It also includes a pair of wings70, the purpose of which will become apparent.

FIG. 5 shows an assembled gearbox 72. A spindle 74 is driven by a motor(not shown). Attached to the spindle 74 is a worm 76, which drives ahelical gear 78. The helical gear then transmits drive via a reductiongear 80 and an idle gear 82 to the gear 64 on the pulley 56. Closelysurrounding over one half of the circumference of the pulley 56 is ashoe 84, the two free ends of which run parallel and close to the edgesof the wings 70 of the doctor 66. The doctor blade 68 is located in the“V”-shaped groove of the pulley 56.

The wings 70 of the doctor 66 define, in conjunction with the gearboxhousing and the shoe 84, an insertion aperture for the cord on each sideof the pulley 56. Installing the cord onto the pulley is simplicityitself. The free end of the cord is offered up to the insertion aperture(under the appropriate wing 70) and the spindle 74 is rotated. The freeend of the cord will then be trapped by a nip 60 in the pulley andbetween the pulley 56 and the shoe 84 and will begin to wind onto thepulley 56. If the cord does not come free of the pulley once it reachesthe other side of the doctor 66, the doctor blade 68 will strip it outof the groove 18. In this sense, the mechanism can be described asself-threading.

As has been explained in detail in the introduction to this application,the use of the pulley and shoe combination described obviates the needfor “back-tensioning” of the cord. In addition, the dimensions of thegroove and the distance between the pulley and the shoe can be optimisedto provide a desired degree of resistance to rotation of the pulley or adesired maximum load rating. Clearly, the first should be as low aspossible so as not to overload the motor; the second should bereasonably high to prevent slippage of the cord in normal use.

With the material and cord specifications as discussed above, a numberof different groove sizes were experimented with, to give an indicationof the amount of leeway available. The groove widths were varied byapplying different amounts of pressure to the two halves of the pulley56 during assembly. The results observed were as follows. “HEIGHT”indicates the maximum and minimum thicknesses of the complete pulley (anindicator of groove width); “TEST CURRENT” is the current draw requiredto drive the gearbox alone; “CORD CURRENT” is the lowest current drawrequired to drive the gearbox and cord; “SLIP CURRENT” is the current atwhich the cord slips in the groove, if held fast; and “LOAD” is the loadin the cord at which the onset of slippage was seen.

TEST CORD CURRENT SLIP HEIGHT CURRENT (mA) LOAD CURRENT (mm) (mA) CW ACW(gm) (mA) 9.00 54 79 86 500+ 9.10 53 69 71 500+ 9.12 55 67 73 500+ 9.1554 66 72 500+ 9.15 55 68 74 500+ 9.15 53 67 71 500+ 9.16 57 67 73 500+9.25 54 62 65 2000+ 500  9.35 53 57 60 600-800 180  9.40 50 57 60400-600 80 9.55 50 57 60 SLIPPED SLIPPED

From these figures, it can be seen that a compromise between good gripand low current draw can be achieved, in this case with a pulleythickness of 9.10-9.25 mm.

What is claimed is:
 1. A method of installing a cord in a cord drivingmechanism of a blind comprising a cord driving pulley having acircumferential, radially outward-facing groove comprising a pluralityof radial nips, the nips defined by formations which are disposedopposite one another on respective sides of the groove and arepositioned so that the path of a cord around the pulley is relativelystraight and so that the cord is substantially unconstricted in theregions between the nips; a doctor defining an insertion opening for thecord, the doctor being arranged adjacent the circumferential groove inthe pulley and adapted to guide the cord out of the groove when thepulley is rotated; and a shoe relative to which the pulley rotates,which surrounds at least part of the circumferential groove in thepulley, the method comprising: inserting a free end of the cord throughthe insertion opening of the doctor into a space defined by thecircumferential groove and the shoe, and offering the free end up to aregion of the groove between two of the nips; rotating the pulley toentrain the cord; and retrieving the free end of the cord once it haspassed around the pulley and is freed by the doctor.
 2. A method ofmotorizing a blind operated by a manual control cord, the methodcomprising: providing motor power to a cord driving mechanism, the corddriving mechanism comprising a cord driving pulley having acircumferential, radially outward-facing groove comprising a pluralityof radial nips, the nips defined by formations which are disposedopposite one another on respective sides of the groove and arepositioned so that the path of a cord around the pulley is relativelystraight and so that the cord is substantially unconstricted in theregions between the nips; and a shoe relative to which the pulleyrotates, which surrounds at least part of the circumferential groove inthe pulley; and offering a free end of the manual control cord to thespace defined by the circumferential groove and the shoe and rotatingthe pulley to entrain the cord.
 3. A method according to claim 2 inwhich the mechanism includes a doctor arranged adjacent thecircumferential groove in the pulley and adapted to guide the cord outof the groove when the pulley is rotated, further comprising retrievingthe free end of the cord once it has passed around the pulley and isfreed by the doctor.
 4. A method according to claim 3 in which thedoctor defines an insertion opening for the cord and the free end of thecord is offered up to that opening.
 5. A method according to claim 2 inwhich the groove comprises a plurality of nips positioned around itscircumference and the free end of the cord is offered up to the regionof the groove between two of the nips.
 6. A control mechanism for ablind comprising a cord for operating the blind; a pulley for drivingthe cord, the pulley having a circumferential, radially outward-facinggroove comprising a plurality of nips the nips, the nips defined byformations which are disposed opposite one another on respective sidesof the groove and are positioned so that the path of a cord around thepulley is relatively straight and so that the cord is substantiallyunconstricted in regions between the nips; a shoe relative to which thepulley rotates, which surrounds at least part of the circumferentialgroove in the pulley; and a motor for transmitting power to the pulley.7. A control mechanism according to claim 6 in which the cord is notback-tensioned.
 8. A control mechanism according to claim 6 in which thecord is retained in the groove by contact with the shoe.
 9. A controlmechanism according to claim 8 in which the dimensions of the groove,the spacing between the groove and the shoe, and the size of the cordare adapted to provide a desired resistance to rotation of the pulleyand a desired maximum load which can be exerted on the cord.
 10. A corddriving mechanism for a blind comprising: a motor; a cord driving pulleyadapted to receive power transmitted from the motor, the pulley having acircumferential, radially outward-facing groove comprising a pluralityof nips, the nips defined by formations which are disposed opposite oneanother on respective sides of the groove and are positioned so that thepath of a cord around the pulley is relatively straight and so that thecord is substantially unconstricted in regions between the nips; and ashoe relative to which the pulley rotates, which surrounds at least partof the circumferential groove in the pulley.
 11. A mechanism accordingto claim 10 in which the shoe surrounds at least half of thecircumference of the pulley.
 12. A mechanism according to claim 10 inwhich the nips are equidistantly spaced around the circumferentialgroove.
 13. A mechanism according to claim 10 in which each of the nipsis radial within the groove.
 14. A mechanism according to claim 10 inwhich the nips are at least four in number.
 15. A mechanism according toclaim 14 in which the nips are twelve in number.
 16. A mechanismaccording to claim 10 in which the formations are triangular teeth. 17.A mechanism according to claim 10 in which the formations are symmetric.18. A mechanism according to claim 10 further including a doctorarranged adjacent the circumferential groove in the pulley and adaptedto guide the cord out of the groove when the pulley is rotated.
 19. Amechanism according to claim 18 in which the doctor is substantiallysymmetric.
 20. A mechanism according to claim 19 in which the doctordefines an insertion opening for the cord.